FIG. 1 illustrates the basic digital mobile communications system architecture. Typically, a mobile communications network comprises at least one core network CN and one or more radio access networks RAN. A core network CN comprises mobile switching centers MSC and possibly other service nodes. A xe2x80x9cnodexe2x80x9d is here a generic name for network components that take part in the switching; thus it also covers mobile switching centers and other exchange equipment. The radio access networks are located between the core network and the terminal equipment. A radio access network comprises base transceiver stations BTS and a radio network controller RNC. Each base transceiver station BTS is connected in a fixed manner with the radio network controller RNC of the radio access network in question. Each radio network controller is in turn connected in a fixed manner with at least one core network node.
The general principle of paging in digital mobile communications networks is according to FIG. 2 as follows. When a call has arrived in a mobile switching center MSC in the traffic area in which the called subscriber is located at that moment, the switching center sends a paging request via radio network controllers to those base transceiver stations in whose area the register data indicate the called subscriber is. The base transceiver stations send the paging message to the radio path on their paging channels PCH. A mobile station that detects its own subscriber identity on a paging channel which it monitors, sends a response to the base transceiver station. This way the network will know the location of the called subscriber with an accuracy of one cell, and the data connection can be established. In this description and in the claims attached hereto, xe2x80x9cdata connectionxe2x80x9d refers to a connection established for the transmitted signal proper. Usually, the most common type of data connection is a voice connection.
In third-generation mobile communications networks, a mobile station may have several international mobile subscriber identities IMSI, and may also have multiple simultaneous data connections under different subscriber identities. If a mobile station has no data connection, an incoming call according tothe prior art always initiates the paging process described above. If the mobile station has a data connection via a given core network node under a subscriber identity, and another node receives a call associated with another subscriber identity of the mobile station, the normal paging process is initiated in this case, too. A disadvantage of this procedure is that, in principle, the network""s signaling capacity is used unnecessarily since the location information of the mobile station in question is already in the network, and that the mobile station possibly has to listen to several paging channels. Arrangements according to the prior art do not support calls directed to one and the same mobile station from different core networks. Establishment of data connections from different core networks to a single mobile station is in principle possible, but it requires that the paging message coming from one of the core networks be distributed to all base transceiver stations and all paging channels, and that the called mobile station listen to all paging channels used in the cell in question. If the paging message is sent only on a given paging channel, it may happen that due to an existing connection the mobile station is unable to listen to the paging channel in question.
An object of the present invention is to minimize the aforementioned disadvantages associated with the prior art. The method according to the invention is characterized by what is expressed in the independent claim. Preferred embodiments of the invention are described in the dependent claims.
The basic idea of the invention is as follows. In a suitable network node, such as the radio network controller RNC of each radio access network, a paging database is created in order to reduce signaling needed for the establishment of data connections. Data useful in connecting the called mobile station are collected in the paging database. For example, when a data connection has been established to a mobile station under a given subscriber identity, the mobile station informs the network in an agreed manner about all the subscriber identities in its use e.g. during call set-up or later during the connection or using e.g. a separate message independent of the possible connections. The network stores these identities in the paging database together with the mobile station location information and signaling connection data possibly associated with said data connection. If, during said connection, the mobile station moves into another cell, the data relating to the mobile station are updated in the paging database. If, during said or a subsequent connection, another subscriber identity of the same mobile station is paged at any node, the network checks the paging database and uses the data found therein to establish a signaling connection.
Advantageously, when the mobile station""s data connection(s) is/are terminated, the data associated with the mobile station are kept in the paging database for at least a certain predetermined period of time after the termination of the connection(s).
An advantage of the invention is that the paging channel load in the cells is reduced since no paging process is needed for the incoming calls, at least not if a data connection already exists at the mobile station. From the mobile station""s point of view this means that during a data connection it does not have to listen to the paging channels. Another advantage of the invention is that when a mobile station is called that has no data connections but has information about it in the database according to the invention, it possibly suffices to send the paging message to one paging channel only. From the point of view of the mobile station this means that it only needs to listen to one paging channel. Yet another advantage of the invention is that connections from different core networks to one and the same radio access network will become practical. This is due to the fact that if a subscriber identity associated with a call coming from an xe2x80x9coutsidexe2x80x9d core network is found in the database according to the invention, the information associated with the identity can be used to direct the paging. For such calls, a mobile station only needs to listen to one paging channel, and not even that in the best case. A further advantage of the invention is that when the general packet radio service GPRS is used, there is no need to transfer subscriber identity information between the mobile switching center MSC and the serving GPRS support node SGSN. A yet further advantage of the invention is that the setting up of simultaneous connections of a mobile station becomes quicker.